The present invention relates to a plate for a fuel cell, in particular for a fuel cell of the type comprising an ion-exchange membrane (PEM), intended to be fitted to a motor vehicle.
Fuel cells of the PEM type generally comprise a stack of bipolar plates and of ion-exchange membranes, the membranes being formed by a solid electrolyte produced, for example, from polymers.
The bipolar plates are provided, on their faces in contact with the membranes, with grooves forming, with said membranes, distribution channels or conduits which allow the gases to move in contact with the membrane.
Anodic gases move on one side of the membrane and cathodic gases move on the opposite side. Oxidation/reduction reactions of the anodic and cathodic gases occur on both sides of the membrane, with exchanges of ions through it, the electrons being conveyed by the bipolar plates. Electrical energy is thus recovered and used, in particular for the traction of the motor vehicle.
When the gases move in the channels from an inlet to an outlet, the reactants are gradually consumed. The concentration of reactants in the stream moving in the channels is thus reduced as the stream moves along. This reduction in reactants, a fortiori close to the distribution channel outlets, can result in a nonuniform distribution of the reactants over the active exchange surface of the membrane. This does not allow satisfactory operation of the cell to be achieved.
Thus, with the aim of obtaining a better performance and an increased reliability of the fuel cell, it is desirable to provide a homogeneous distribution of the anodic and cathodic reactants over the active regions of the membranes.
Various solutions have already been devised in order to obtain a better distribution of the reactants. Thus it is that U.S. Pat. No. 4,988,583 describes a bipolar plate provided, on one of its faces, with a single channel for the distribution of fluids which makes its way from one edge of the plate to an opposite edge and which is produced from a plurality of continuous meanders spread out in boustrophedon form. The meanders are arranged on the face of the plate so as to be distributed over most of said face.
U.S. Pat. No. 5,641,586 for its part describes a bipolar plate comprising a plurality of inlet channels and outlet channels for fluids arranged between one another in intersected fashion, the fluids moving from the inlet channels to the outlet channels while passing through a gas diffusion layer.
In addition, the documents U.S. Pat. No. 6,616,327 and U.S. Pat. No. 6,333,019 describe an arrangement of feed and/or discharge conduits for fluids, in particular for a fuel cell comprising a stack of plates, in which inlet and outlet sections are inserted onto each of the plates so as to obtain fluid circulation conduits exhibiting a staged fractal configuration.
In addition, the documents US-A-2004/0023100 and US 2004/0067405 describe a bipolar plate comprising feed and/or discharge conduits for fluids provided with a main branch and with successive side branches, with a reduced cross section with respect to said main conduit, and arranged so as to obtain conduits exhibiting a fractal configuration.
The channels or conduits for feeding and/or discharging fluids described in these documents do not provide an arrangement which makes it possible to significantly improve a distribution of reactants in order to obtain a homogeneous distribution of the reactants on the membrane.